This invention relates generally to a hypodermic injection apparatus, and more specifically to such an apparatus having a replaceable ampule unit carrying a plunger and a power source for administering intramuscular and subcutaneous injections without a needle.
Present needleless hypodermic injection apparatus involve the use of separately and independently replaceable ampule units and power source units containing CO.sub.2 cartridges. An example of such a unit is described in U.S. Pat. No. 3,688,765 issued to Gasaway on Sept. 5, 1972. The device described in that patent includes a central body. On one end of the body is disposed an ampule unit having a generally cylindrical chamber and a plunger disposed in one end spaced away from a nozzle disposed in the other end. Abutting a side of the plunger opposite from the nozzle is the end of a piston which extends through a passageway to an opposite end of the body. A pressurized-gas cartridge is attached to the opposite end of the body with a frangible seal accessible from the center of the body. A firing pin is spring-loaded to be projected into the CO.sub.2 cartridge for release of the gas contained therein. The firing pin is hollow to conduct escaping gas into a cylinder which houses the plunger-driving piston described earlier. The piston thus drives the plunger toward the nozzle, expelling medication contained in the ampule unit.
Such a unit requires separate loading of the pressurized-gas cartridge and the medication-containing ampule. Two members of the apparatus must be relatively rotated and axially pulled away from each other in order to cock the device. Further, the piston which drives against the plunger during ejection of the medication is exposed to the air during changing of an ampule unit. Such units thus require a fair amount of physical manipulation by the physician or other medical attendant. Also, there is some chance of infecting the ampule unit, either through its nozzle or through the plunger.
Another type of needleless hypodermic injection device is disclosed in U.S. Pat. No. 4,089,334 to Schwebel et al. This patent discloses a device which uses a pyrotechnic cap which, when detonated, provides an explosive charge of gas which drives medication through a discharge aperture in one end of the device. There are many drawbacks inherent in the use of this type of device, including danger to the patient, or at least apprehension of such danger. Because of this danger or at least the perception of such danger, this device will often not be usable in soft-tissue areas of the body, such as the mouth, where the patient may be particularly sensitive to use of an explosive device.
It is therefore a general object of the present invention to overcome the drawbacks and limitations of the prior art proposals. More particularly, the invention has as its objects, the following: (1) to provide a needleless hypodermic injection apparatus which requires only replacement of a single ampule unit containing a power source, plunger and medication ampule; (2) the provision of such an apparatus which may be operated by one having little expertise or training in the use of such devices; (3) the provision of a needleless hypodermic injector which is automatically re-cocked after each use thereof; (4) to provide a hypodermic injection apparatus having a plurality of components, which is not usable unless the components are properly and fully assembled; (5) to develop a needleless hypodermic injection device which is usable in close proximity to the soft-tissue areas of the body, such as the mouth, due to the minimization of actuation noises and expulsion of gases during the injection process; (6) the provision of an injection device which is able to inject medication into the tongue so that the medication reaches the bloodstream at the earliest possible moment; and (7) to provide a needleless hypodermic injection apparatus which is simple in construction and therefore relatively easy and inexpensive to fabricate and assemble and which therefore may be marketed in both reusable and disposable embodiments.